1. Field of the Invention
The present invention relates to a lens driving device which has an auto focus function and a shaking correction function and is applied to cameras for mobile phones.
2. Description of Related Art
A lens driving device with the functions of auto focus and shaking (unintentional movement) correction (hereafter called lens driving device) is composed of the following components: an auto focus unit which enables a lens loaded in a camera to move forward, move backward or focus towards an object to be shot positioned in front of the lens and a shaking correction unit for inhibiting a shot image from generating drifting due to shaking.
For example, the Japanese patent application No. P2011-65140A (publication date Mar. 31, 2011) discloses a lens driving device with the functions of auto focus and shaking correction, namely an auto focus unit enables a lens maintained on a lens carrier to move along a focus direction, and a shaking correction unit enables the auto focus unit to swing in directions forming a right angle with an optical axis (the focus direction), so that the image generated on an image sensor is inhibited from shifting. Moreover, the optical axis direction of the lens is set to be Z direction (Z side), the side of the object to be shot is set to be the front of the Z direction (+Z side), and the two directions which form a right angle with the Z direction and are mutually orthogonal are set to be X direction and Y direction.
As shown in FIG. 6A and FIG. 6B, the lens driving device 69 includes the auto focus unit 50 and the shaking correction unit 60. The auto focus unit 50 is composed of the lens carrier 54 for maintaining the lens 53, a coil 55 for focus, a magnet support 68, four magnets 52, two spring components 57 and a base 56 for focus.
The coil 55 formed in the shape of an octagonal ring is wound around the Z direction (axis) and are mounted on the lens carrier 54. Each magnet 52 is formed in the shape of a square plate, and a plurality of magnets 52 are annularly configured on the outer side in the radial direction of the coil 55 at 90-degree intervals along the X side and the Y side respectively. The magnets 52 are arranged opposite to the coil 55 at intervals along the radial direction. The magnet support 68 is formed in the shape of an octagonal frame and is used for maintaining the magnets 52.
The spring components 57 are composed of a front side spring component 57A and a back side spring component 57B. The front side spring component 57A and the back side spring component 57B are plate springs extending along the X direction and the Y direction.
Each of the front side spring component 57A and the back side spring component 57B includes an inner side maintaining part 57a (unshown on the back side spring component 57B), an outer side maintaining part 57b and a wrist part 57c. The inner side maintaining parts 57a are circularly formed on the inner peripheral sides of the front side spring component 57A and the back side spring component 57B. Moreover, the outer side maintaining parts 57b are squarely formed on the outer peripheral sides of the front side spring component 57A and the back side spring component 57B. Moreover, each wrist part 57c extends along the peripheral direction and the radial direction alternately in a zigzag manner, one end of each wrist part is connected with a corresponding inner side maintaining part 57a, and the other end of each wrist part is connected with a corresponding outer side maintaining part 57b. 
The inner side maintaining part 57a of the front side spring component 57A is connected with the front side end part of the lens carrier 54, and the outer side maintaining part 57b of the front side spring component 57A is connected with the front side end part of the magnet support 68. The inner side maintaining part 57a of the back side spring component 57B is connected with the back side end part of the lens carrier 54, and the outer side maintaining part 57b of the back side spring component 57B is clamped between the back side end part of the magnet support 68 and the base for focus 56.
The shaking correction unit 60 is composed of a frame 61, a base 62 for swinging the lens, four suspension wires 63, a shielding box 64 and coils 65x, 65y for swinging the lens. The frame 61 is formed in the shape of a square frame, is configured in front of the auto focus unit 50, and is connected with the magnet support 68. The base 62 is formed in the shape of a square plate, a circular opening is defined in the central part of the base 62, and the base 62 is configured at the back of the auto focus unit 50 at an interval.
The suspension wires 63 extends along the Z direction, one end of the suspension wires 63 is connected with the frame 61, and the other end of the suspension wires 63 is connected with the base 62, so that the auto focus unit 50 can be supported in a swing and suspension manner in the X direction and the Y direction.
The circular opening is formed in the front surface of the shielding box 64 which wraps the outer side and the front side of the auto focus unit 50 in the radial direction. The coil 65x and the coil 65y are mounted on the inner side of the side walls of the shielding box 64. The coil 65x is wound around the X direction (axis) and is mounted on the inner side of the X-side-side wall of the shielding box 64, and the coil 65x and the magnets 52 are arranged opposite to each other at intervals along the radial direction. Moreover, the coil 65y is wound around the Y direction (axis) and is mounted on the inner side of the Y-side-side wall of the Y side of the shielding box 64, and the coil 65y and the magnets 52 are arranged opposite to each other at intervals along the radial direction.
Thus, the magnets 52 and the coil 55 are combined so as to form a drive mechanism for the auto focus unit 50. Moreover, the magnets 52 are combined with the coils 65x, 65y so as to form a drive mechanism for the shaking correction unit 60. In other words, the magnets 52 play two roles of focus and shaking correction.
And then, along with the inflow of current for focus, under the action of a magnetic field applied by the magnets 52, lorentz force is generated along the Z direction by the coil 55. As a result, the lens carrier 54 supported on the spring components 57 in a suspension manner moves towards the Z direction.
Moreover, along with the inflow of current for shaking correction, under the action of the magnetic field applied by the magnets 52, lorentz force is generated along the Y direction and the X direction by the coil 65x and the coil 65y, and counter-acting force is generated by the magnets 52 in response to the lorentz force. As a result, the magnets 52 enable the auto focus unit 50 to swing in a direction opposite to the lorentz force generated by the coil 65x and the coil 65y. 
Moreover, a position sensor 67 is mounted on a base 62 positioned at the back of the magnets 52 in the Z direction. When a shake/shakes happens, the position sensor 67 measures a distance that the shaking correction unit 60 swings in the direction forming the right angle with the Z axis.
The lens driving device 69 can play the role of shaking correction just by utilizing the simple structure of the auto focus unit 50 suspended by the suspension wires 63. Moreover, the lens driving device also has the advantage of easy assembly.
However, in the lens driving device 69, the suspension wires 63 need to directly support the auto focus unit 50 formed by overlapping the lens 53, the lens carrier 54, the coil 55, the magnet support 68, the magnets 52, the spring components 57 and the base 56. Therefore, when the lens driving device suffers from external force such as impact force in the Z direction, the impact force can be transmitted onto the auto focus unit 50 or the suspension wires 63; after the suspension wires 63 suffers from the impact, the problem that breakage or buckling damages the function of the shaking correction unit 60 may appear due to the fact that the tension or compressing force cannot be alleviated.